Catheter steering assembly providing asymmetric left and right curve configurations

ABSTRACT

A catheter has an electrode tip assembly that is bendable at the selection of the user in two different directions. The electrode tip assembly assumes different asymmetric predetermined curve configurations when bent in the two directions and is manipulated by means of steering wires adjustably connected tangentially to the lateral edges of a rotatable cam located in the catheter handle.

This is a continuation of application Ser. No. 08/632,762 filed on Apr.16, 1996 ; now abandoned, which is a continuation of application Ser.No. 08/324,585 filed on Oct. 18, 1994 (now abandoned); which is acontinuation of application Ser. No. 08/058,319 filed on May 6, 1993(now U.S. Pat. No. 5,358,478), which is a continuation-in-part ofapplication Ser. No. 07/790,207 filed Nov. 8, 1991, now (U.S. Pat. No.5,273,535) and a continuation-in-part of application Ser. No.07/991,474, filed Dec. 16, 1992, now U.S. Pat. No. 5,254,088, which is acontinuation of Ser. No. 07/736,384, filed Jul. 26, 1991, (nowabandoned) which is a divisional of application Ser. No. 07/473,667,filed Feb. 2, 1990, (now abandoned).

FIELD OF THE INVENTION

The invention generally relates to steering controls for catheters. In amore specific sense, the invention relates to catheters that can besteered and manipulated within interior regions of the body from alocation outside the body.

BACKGROUND OF THE INVENTION

Physicians make widespread use of catheters today in medical proceduresto gain access into interior regions of the body. It is important thatthe physician can control carefully and precisely the movement of thecatheter within the body, especially during procedures that ablatetissue within the heart. These procedures, called electrophysiologicaltherapy, are becoming more widespread for treating cardiac rhythmdisturbances.

During these procedures, a physician steers a catheter through a mainvein or artery (which is typically the femoral artery) into the interiorregion of the heart that is to be treated. The physician then furthermanipulates a steering mechanism to place the electrode carried on thetip of the catheter into direct contact with the tissue that is to beablated. The physician directs radio frequency energy into the electrodetip to ablate the tissue and form a lesion.

Cardiac ablation especially requires the ability to precisely bend andshape the tip end of the catheter to position the ablation electrode.

SUMMARY OF THE INVENTION

The invention provides a catheter having a distal tip section that isbendable at the selection of the user in two different directions. Thedistal tip section assumes different predetermined curves when bent ineach direction. The degree of bending or shape of the predeterminedcurve can be adjusted in accordance with the invention.

The invention provides a catheter having a body that is bendable indifferent first and second directions in response to external forces.The catheter includes a steering mechanism that is movable in two pathsfor applying different external bending forces on the body and whereinthe forces can be adjusted by providing for a different length of travelpaths for causing bending forces in the first and second directions.

The steering mechanism includes a first actuator that operates inresponse to movement of the steering mechanism in the first path. Thefirst actuator bends the body in the first direction into a firstadjustable predetermined nonlinear shape.

The steering mechanism also includes a second actuator that operates inresponse to movement of the steering mechanism in the second path. Thesecond actuator bends the body in the second direction into a secondadjustable predetermined nonlinear shape. The second shape is differentfrom the first shape.

In one embodiment, the bendable body includes a flexible wire memberhaving left and right faces. In this arrangement, the steering mechanismincludes left and right steering wires. The distal ends of the steeringwires are attached, respectively, to the left and right faces of thewire member.

In this embodiment, the first actuator places the left steering wireinto tension to bend the wire member to the left into the firstadjustable nonlinear shape. The second actuator places the rightsteering wire into tension to bend the wire member to the right into thesecond adjustable nonlinear shape. The steering wires cause asymmetricbending of the wire member by virtue of the fact that the first andsecond actuators cause the left and right steering wires to traveldifferent distances.

In one embodiment, the points of attachment of the distal ends of theleft and right steering wires are generally symmetrically spaced on theleft and right faces of the wire member. In another arrangement, thepoints of attachment of the distal ends of the left and right steeringwires are generally asymmetrically spaced on the left and right faces ofthe wire member.

In one embodiment, the steering mechanism includes a rotatable cam tothe lateral edges of which the proximal ends of the left and rightsteering wires are adjustably attached. A lever mechanism rotates therotatable cam to the left and to the right.

In this arrangement, the first actuator includes a first cam surfaceformed on the left side of the rotatable cam. The first cam surfacebears against and tensions the left steering wire in response torotation of the rotatable cam to the left.

Also in this arrangement, the second actuator includes a second camsurface formed on the right side of the rotatable cam. The second camsurface is configured differently from the first cam surface and bearsagainst and tensions the right steering wire in response to rotation ofthe rotatable cam to the right.

In one embodiment, the first and second cam faces form curves havingdifferent radii. Alternatively, the cam faces may be symmetrical butasymmetric steering is accomplished by adjusting the amount of travel ofthe steering wires.

The steering wires are preferably attached tangentially to the lateraledges of the rotatable cam and can be adjusted so that rotation of therotatable cam results in a multitude of selectable different left andright curve shapes. In accordance with the preferred embodiment of theinvention the control wires extend through adjustable stop membersthreaded into threaded openings in the lateral edges of the rotatablecam. The proximal ends of the wires are fixed to terminal blocks thatare engaged by the stops upon rotation of the rotatable cam to therebyselectively apply tension to the wires. Preferably the steering wiresare attached to the terminal blocks by having the ends thereof beingbent at an angle exceeding 90°, in fishhook fashion, and being solderedinto the blocks.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a catheter that embodies the features ofthe invention;

FIG. 2 is a top central sectional view of the handle portion of thecatheter of FIG. 1 taken generally along Line 2--2 with parts brokenaway for clarity;

FIG. 3 is an exploded view of the electrode tip assembly of thecatheter;

FIG. 4 is a perspective view of the stiffening assembly for the supportwire of the catheter;

FIG. 5 is a top view of the catheter in the unbent position with partsbroken away to show the steering mechanism;

FIG. 6 is top view of the catheter of FIG. 5 steered to the left;

FIG. 7 is a top view of the catheter of FIG. 5 with the steeringmechanism adjusted to a different setting and steered to the left at adifferent curvature;

FIG. 8 shows the steering mechanism of the catheter with partsdisassembled for clarity;

FIG. 9 is a top view of a rotatable cam used in the steering mechanism;

FIG. 10 is a perspective view of the cam shown in FIG. 9;

FIG. 11 is a cross sectional view of the steering wire terminal of thesteering mechanism; and,

FIG. 12 is a cross sectional view taken along Line 12--12 of FIG. 8showing the adjustable stop used in the steering mechanism.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a steerable catheter 10 that embodies the features of theinvention. As there shown, the catheter 10 includes three main parts orassemblies: the handle assembly 12, the guide tube assembly 14, and theelectrode tip assembly 16. An electrical cable 48 for providing power toan electrode at the distal tip of the catheter attaches to the back ofthe housing 20.

The catheter 10 can be used in many different environments. Thisspecification will describe the catheter 10 as used to provideelectrophysiologic therapy in the interior regions of the heart.

When used for this purpose, a physician grips the handle assembly 12 tosteer the guide tube assembly 14 through a main vein or artery (which istypically the femoral arterial) into the interior region of the heartthat is to be treated. The physician then further manipulates a steeringmechanism 18 on the handle assembly 12 (which will be described later)to place the electrode tip assembly 16 in contact with the tissue thatis to be ablated. The physician directs radio frequency energy into theelectrode tip assembly 16 to ablate the tissue contacting the electrodetip assembly 16.

As FIG. 2 best shows the handle assembly 12 includes a housing 20 thatencloses the steering mechanism 18. The steering mechanism 18 includes arotatable cam 23 carried on a screw 24 within the housing 20. Therotatable cam 23 is seated for rotation between top washer 26 whichbears on a shoulder 27 and a bottom washer. Screw 24 is threaded into acentral opening in washer 26. An external steering lever 34 isadhesively bonded or ultrasonically welded to the top of the rotatablecam 23. A tab 35 on the steering lever 34 is seated in a notch 37 inrotatable cam 23. The steering lever 34 also seats against an O-ring(not shown). Further details regarded the O-rings and similar assemblydetails are described in the above-mentioned copending application Ser.No. 790,207, the entire disclosure of which is herein incorporated byreference.

Movement of the steering lever 34 by the user rotates the rotatable cam23 about the screw 24 within the housing 20. Clockwise movement of thesteering level rotates the rotatable cam 23 to the right.Counterclockwise movement of the steering wheel rotates the rotatablecam 23 to the left. Contact between the steering lever 34 and the sideof the housing 20 physically limits the range of left and right rotationof the rotatable cam 23 within the housing 20.

The steering mechanism 18 also includes an external locking lever 38which is provided with a hexagonal opening into which the hexagonal headof the screw 24 is seated and bonded by an adhesive. The locking lever38 seats against another O-ring. Movement of the locking lever 38rotates the screw 24 in the threaded opening in washer 26. Clockwiserotation of the locking lever 38 tightens the screw 24 to increase theseating force on the rotatable cam 23. When moved fully clockwise intocontact against the housing 20, the locking lever 38 imposes a seatingforce that restricts rotation of the rotatable cam 23 by the steeringlever 34. Counterclockwise movement of the locking lever 34 loosens thescrew 24 to decrease the seating force and free the rotatable cam 23 forrotation.

The rotatable cam 23 includes an asymmetrically shaped forward cam face41. The forward cam face 41 is oriented toward the front of the housing20, where the guide tube assembly 14 attaches. The forward cam faceincludes a right side cam surface 44 and a left side cam surface 46.Surfaces 44 and 46 are located at the bottoms of grooves in the lateraledges of rotatable cam 23. Surfaces 44 and 46 may either be of the same(symmetric) radii or may be asymmetrically shaped. In the formerinstance asymmetric steering of the catheter distal tip is accomplishedby adjusting the distance traveled by the steering wires and, as aresult, the amount of tension applied thereto.

The rotatable cam 23 is provided on its lateral edges with threadedholes 51 and 53 into which adjustable stops 55 and 57, respectively, arethreaded. The proximal ends of right and left catheter steering wires 56and 58, pass through central openings in stops 55 and 57 and areattached to steering wire terminals 59 and 61. Steering wires 56 and 58are bent in fishhook fashion (at an angle greater than 90° at theirproximal ends 65 and are soldered (67) to the interior of the terminalblocks 59 and 61 (as best seen in FIGS. 8 and 11) in order to firmlyanchor the wire ends within the terminal blocks. In order to facilitateadjustment of stops 55 and 57, they are provided with a flattenedproximal end 63 which can be engaged by a wrench or similar tool inorder to rotate the stops and thus adjust the distance that the stopsextend proximally from the edges of rotatable cam 23.

The steering wires 56 and 58 extend from the stops 55 and 57 along theassociated left and right side surfaces 44 and 46 of the cam face 41.The steering wires exit the front of the housing 20 through the interiorbore of a tension screw assembly 60.

As will be described in greater detail later, the distal ends of thesteering wires 56 and 58 are attached to the electrode tip assembly 16.They extend from the tension screw assembly 60 through the guide tubeassembly 14 to the electrode tip assembly 16.

As also will be described in greater detail, the adjustable wire stops55, 57 in association with the terminal blocks 59, 61 and cam faces 44and 46 translate rotation of the rotatable cam 23 into lateral pullingmovement of the steering wires 56 and 58 attached to the electrode tipassembly 16.

By rotating the rotatable cam 23 to the left as shown in FIG. 6 (bymoving the steering lever 34 counterclockwise), the left steering wirestop 55 bears against the left terminal block 59 and cam surface 46.This movement tensions the left steering wire 58 to impose a discrete,constant pulling force that causes the electrode tip assembly 16 to bendto the left in a desired curvature. If a different degree of curvatureis desired, for example, as shown in FIG. 7, stop 55 is rotated toextend it distally, thus adjusting the curvature as shown. Also, sincecam surface 44 and 46 are asymmetric in shape, the range of possiblecurvatures is different for the right and left wires. Thus a nearlyinfinite variety of asymmetric curve shapes is possible by adjustment ofthe stops. In practice, catheters having a standard number of presetasymmetric curvatures can be factory produced, all using exactly thesame component parts.

By rotating the rotatable cam 23 to the right (by moving the steeringlever 34 clockwise), tension is applied to the right steering wire 56 inexactly the same manner as described in connection with wire 58, causingthe electrode tip assembly 16 to bend to the right.

Rotation of the tension screw assembly 60 additionally varies the amountof slack (i.e., tension) in the steering wires 56 and 58. This controlsthe responsiveness of the electrode tip assembly 16 to rotation of therotatable cam 23.

The component parts of the handle assembly 12 can be constructed ofvarious materials, depending upon the durability needed and thesterilization process used. For example, when ETO sterilization is used,the housing 20 and bottom washer 28 can be made of a polycarbonatematerial. In this arrangement, the rotatable cam 23, steering lever 34,and locking lever 38 can be made of a Delrin material. These plasticmaterials are durable and EtO sterilizable. In this assembly, the nuts,pins, and screw 24 are preferably made of a corrosion resistant metallicmaterial such as brass or stainless steel.

As FIG. 3 shows, the guide tube assembly 14 includes a flexible shaft 62attached to the handle assembly 12. The flexible shaft 62 encloses aninterior bore 64. The steering wires 56 and 58 pass through the interiorbore 64.

The shaft 62 may constructed in various ways. In the embodiment shown inFIG. 3, the shaft 62 comprises a length of stainless steel coiled into aflexible spring enclosing the interior bore 64. A sheath 66 of extrudedplastic material containing wire braids encloses the coil. The sheath 66is preferably made from a thermoplastic material, such as apolyurethane, a polyolefin or polyetherpolyamide block copolymer.

Alternatively the shaft 62 comprises a slotted, stainless steel tubeenclosing the interior bore. Further details of such slotted shafts aredisclosed in pending Lundquist U.S. patent application Ser. No.07/657,106 filed Feb. 15, 1991 and entitled "Torquable Catheter 10 andMethod."

The handle assembly 12 includes a tubular stem 74 though which theproximal end of the guide tube assembly 14 extends for attachment to thetension screw assembly 60. Adhesive attaches the proximal end of braidedsheath 66 to stem 74. The guide tube assembly 14 can be made in variouslengths. In the case of cardiac ablation catheters, the guide tubeassembly 14 is usually about 100 cm in length.

As FIGS. 1 and 2 show, a sleeve 76 couples the guide tube assembly 14 tothe handle assembly 12. Adhesive secures one end of the sleeve 76 to thehandle stem 74. The sleeve 76 includes an interior bore thatprogressively tapers from the handle stem 74 into a tight interferencefit about the sheath 66 of the guide tube assembly 14. The exterior ofthe sleeve 76 also tapers, extending about 4 to 5 inches beyond thefront of the handle housing 20.

The sleeve 76 is made of a material having a high coefficient offriction, like Krayton G2703. The sleeve 76 provides a gripping surfaceto help the user manipulate the catheter 10. When used in associationwith the slotted tube, the sleeve 76 also significantly enhances thetransmission of torque from the handle assembly 12 to the electrode tipassembly 16 through the guide tube assembly 14.

The electrode tip assembly 16 includes a bendable main support wire orspring 78 having left and right faces 78L and 78R. In the illustratedembodiment, the main support wire 78 is made of stainless steel flatwire stock in an elongated shape about 0.035 inch wide and about 0.005inch thick. The main support wire 78 is about 3 inches in total length.

The opposite ends of the main support wire 78 are cut away to formstepped shoulders 80 and 82. In the illustrated embodiment, theshoulders 80 and 82 are about 0.024 inch wide and aligned along thecenterline of the main support wire 78. Each shoulder 80 and 82 is about0.12 inch in length.

As FIG. 3 shows, one stepped shoulder 80 fits within the distal end ofthe flexible guide tube shaft 62 to append the electrode tip assembly 16to the guide tube assembly 14. When properly oriented, the left andright faces 78L and 78R of the main support wire 78 lie in planes whichare generally parallel to the axis about which the rotatable cam 23rotates. Stated differently, when the user holds the handle assembly 12in a horizontal plane, the left and right faces 78L and 78R of the mainsupport wire 78 lie in a vertical plane.

As FIG. 3 shows, the distal end of the left steering wire 58 is solderedto the left face 78L of the main support wire 78. When pulled by leftrotation of the rotatable cam 23, the left steering wire 58 bends themain support wire 78 to the left.

Also, the distal end of the right steering wire 56 is soldered to theright face 78R of the main support wire 78. When pulled by rightrotation of the rotatable cam 23, the right steering wire 56 bends themain support wire 78 to the right.

In the illustrated embodiment, the stiffness of the main support wire 78is not uniform, but varies along its length. Its stiffest point is nearits proximal end region, where it joins the guide tube shaft 62. Itsstiffness is least at the tip end 88 of the shoulder 82. By varying thestiffness of the main support wire 78 between its proximal end and itsdistal tip end 88, the base of the electrode tip assembly 16 (where itjoins the guide tube assembly 14) resists bending and buckling. Thebending forces generated by the steering wires 56 and 58 are directedtoward the distal tip end 88 of the main support wire 78. The variablestiffness of the main support wire 78 concentrates the bending forces atthe distal tip end 88 of the electrode tip assembly 16.

There are various ways to varying the stiffness of the main support wire78 along its length. One way (not shown) is to vary the thickness of themain support wire 78 as it is manufactured, so that it is thickest(i.e., most stiff) near the shoulder 80 that, in use, is fitted withinthe guide tube shaft 62.

In the illustrated and preferred embodiment (see FIG. 4), a stiffeningspring assembly 90 stiffens the center support near the distal end ofthe guide tube shaft 62. The stiffening spring assembly 90 includes twoleaf springs 92 that sandwich the main support wire 78 between them.Each leaf spring 92 is made of stainless steel flat wire stock in anelongated shape that is about 0.035 inch wide and about 0.0025 inchthick.

The stiffening spring assembly 90 can be sized and configured to providethe degrees of stiffness and variance wanted. In the illustratedembodiment, the stiffening spring assembly 90 stiffens the main supportwire 78 beginning about 0.030 to 0.050 inch from the inner edge of theattachment shoulder 80 and extending from there about 1.5 inches.

In the illustrated embodiment, spot welds 94 secure the leaf springs 92to the main support wire 78. The three spot welds 94 shown are clusterednear the proximal end of the stiffening spring assembly 90. There, theyare evenly spaced, with the most distal spot weld 94 being about 0.10inch from the proximal end of the stiffening spring assembly 90.

In the illustrated embodiment, the distal end of the electrode tipassembly 16 carries an ablation tip electrode 96 and three ringelectrodes 98. Interior conducting wires 100 are connected to the tipelectrode 96 and the three ring electrodes 98. The conducting wires 100extend along the main support wire 78, through the interior bore of theguide tube shaft 62, and into the handle housing 20 to join the cable 48that extends from the rear of the housing 20.

The cable 48 ends with plugs 102. The plugs 102 connect with appropriateconventional catheter control equipment (not shown). The conductingwires 100 transfer electrical current from the ring electrodes 98indicative of electrical activity within the heart. The conducting wires100 also transfer radio frequency energy to the tip electrode 96 tocarry out ablation procedures within the heart.

There are various ways of securing the attachment between the electrodetip assembly 16 and the guide tube assembly 14. The illustratedembodiment employs a reinforcing sleeve assembly 104 for this purpose.The reinforcing sleeve assembly 104 holds the steering wires 56 and 58in close intimate contact against the main support wire 78. Isolation ofthe conducting wires 100 from the steering wires 56 and 58 preventskinking and chafing of the conducting wires 100 during bendingoperations.

The materials used to make the reinforcing sleeve assembly 104 can vary.Shrink tubes 114 can be made from medical grade TFE Teflon materialhaving a 2 to 1 shrink ratio. A reinforcing fabric 116 is wrapped intension over first tube 114 as a single spiral about the tube 114 toobtain a desired, closely spaced pitch. In the illustrated embodimentthe fabric 116 is wrapped to a pitch of about 18 to 20 wraps per inch.The preferred material has a wall thickness (after heat shrinkage) ofabout 0.003 to 0.0045 inch. In the illustrated embodiment, the fabric116 is a Kevlar 49 Yarn (which is available from DuPont). This materialhas a tensile strength of about 410,000 lbs/in² and a modulus of about18,000,000 lbs/in².

An outer tube 120 covers the reinforcing sleeve assembly 104. The tipelectrode 96 is soldered to the center support 78 and ring electrodes 98are attached to the conducting wires 100 and joined to the outer tube120 by conventional methods to complete the electrode tip assembly 16.

In the illustrated embodiment, the curvature assumed upon bending theelectrode tip assembly 16 to the left is different than the curvatureassumed upon bending the electrode tip assembly 16 to the right. Theelectrode tip assembly 16 assumes one curvature when bent to the leftand a different curvature when bent to the right. These different leftand right curvatures provide the physician with flexibility in steeringthe tip electrode 96 into position. These differing curvatures asreferred to herein as asymmetric curves.

In addition to the use of a rotatable cam to cause different amounts oftravel of the left and right steering wires, it is contemplated thatsuch different amounts of travel can also be caused by means of othermechanisms, as well. For example, a rotatable gear can be intermeshedwith a pair of movable toothed racks to form a rack and pinionarrangement. In such case the two racks can be configured differently,or provided with stops to limit the travel in one direction more than inthe other.

Various features of the invention are set forth in the following claims.

What is claimed is:
 1. A catheter having an elongated tubular bodybendable adjacent to its distal end in response to an external force,and a proximal end attached to a handle for manipulating said tubularbody by applying the external force thereto, comprising,a steeringassembly for applying a bending force on the body, the steering assemblyincluding a rotatable cam located in said handle, a steering wireoperable in response to movement of the rotatable cam for bending thetubular body, said steering wire being attached tangentially to thelateral edges of said rotatable cam by a means for connection, saidmeans for connection of said wire being adjustable so that thecorresponding degree of movement of said tubular body in response torotation of said rotatable cam is altered by adjustment of saidconnection.
 2. A catheter according to claim 1 further including aflexible guide tube having a distal end attached to said tubular bodyand a proximal end attached to said steering assembly, said guide tubeincluding a flexible shaft having an interior bore formed from a lengthof wire coiled into a flexible spring, said interior bore enclosing saidsteering wires.
 3. A catheter according to claim 1 wherein said meansfor connection comprises a threaded member which is attached to a matingthreaded socket on said cam.
 4. A catheter according to claim 1 whereinsaid means for connection comprises an adjustable stop member which isthreaded into a threaded opening provided in the lateral edge of saidrotatable cam, the proximal end of said wire including a terminal block,said adjustable stop member being engaged by said terminal block uponrotation of said rotatable cam to apply tension to said wire.
 5. Acatheter according to claim 1 wherein said means for connectioncomprises a threaded member, and a mating threaded socket on said cam,said threaded member and said threaded socket being threadedly attachedto each other.
 6. A catheter having an elongated tubular body bendableadjacent to its distal end in different first and second directions inresponse to external forces, and a proximal end attached to a handle formanipulating said tubular body by applying the external forces theretocomprising,a steering assembly for applying bending forces on the body,the steering assembly includinga rotatable cam located in said handle, afirst steering wire and a second steering wire operable in response tomovement of the rotatable cam for bending the tubular body in a firstdirection into a first non-linear configuration and in a seconddirection into a second predetermined nonlinear configuration, each ofsaid steering wires being attached tangentially to the lateral edges ofsaid rotatable cam by a separated, stop member for each wire, said stopmember of each wire being adjustable so that the degree of movement ofeach said wire in response to rotation of said rotatable cam is alteredby adjustment of said each stop member.
 7. A catheter according to claim6further including a guide tube having a distal end attached to saidbody and a proximal end attached to said steering assembly.
 8. Acatheter according to claim 6wherein said body includes a flexible wiremember having left and right faces, wherein said steering assemblyincludes left and right steering wires having distal ends attached,respectively, to the left and right faces of the wire member, whereintension applied to the left steering wire causes bending of the wiremember to the left into the first nonlinear configuration, and whereintension applied to the right steering wire causes bending of the wiremember to the right into the second nonlinear configuration.
 9. Acatheter according to claim 6 wherein said each stop member comprises athreaded member, and a mating threaded socket on said cam, said threadedmember and said threaded socket being threadedly attached to each other.10. A catheter according to claim 6 wherein said each stop membercomprises independently adjustable stop members which are threaded intothreaded openings provided in the lateral edges of said rotatable cam,the proximal ends of said wires including terminal blocks, saidadjustable stop members being engaged by said terminal blocks uponrotation of said rotatable cam to apply tension to said wires.
 11. Acatheter according to claim 6wherein the rotatable cam comprises firstand second cam faces that are formed as curves having different radii.12. A catheter having an elongated tubular body, said body having alongitudinal axis and being bendable adjacent its distal end in responseto external forces, and having a proximal end attached to a handle formanipulating said tubular body by applying the external forces thereto,comprising,a steering assembly for applying bending forces on the body,the steering assembly including a movable component located in saidhandle, a steering wire operable in response to movement of said movablecomponent for bending the tubular body in a first direction into anon-linear configuration, said steering wire having a longitudinal axisbeing adjustably connected to said movable component by a stop member onthe movable component, said stop member being adjustable in a directionparallel to the longitudinal axis of said steering wire whereby thedegree of movement of said steering wire in response to movement of saidmovable component is altered by adjustment of said stop memberconnection.
 13. A catheter according to claim 12 wherein said stopmember comprises a member which is threaded into a threaded opening insaid movable component.
 14. A catheter according to claim 12 whereinsaid movable component comprises a rotatable cam.